Thickness determination of low doped SiC epi-films on highly doped SiC substrates

The room temperature infrared reflectance of low doped SiC epi-films, both 4H and 6H polytypes, deposited by chemical vapor deposition on highly doped SiC substrates has been measured. The epi-film doping levels are in the 10¹⁵ cm⁻³ range while the substrate doping levels are in the 10¹⁸ to 10¹⁹ cm⁻³ range. Interference fringes from the epi-films are often observed in the frequency region below the reststrahl band in SiC (200–600 cm⁻¹) and they can be used to determine the thickness of these epi-films. The fringes arise due to the difference in free carrier concentration between the epi-film and substrate which causes differences in their frequency dependent dielectric functions. The epi-film thickness determinations were made by comparison of the measured infrared reflectance spectra to calculated spectra based on a frequency dependent dielectric function modeled with Lorentz oscillators using only bulk input parameters. The effects of film and substrate anisotropy and off normal incidence are included in the calculation.